THE HAGUE/FEODOSIA, Ukraine - US President Barack Obama began crisis talks with his European allies on Monday after Ukraine announced the evacuation of its troops from Crimea, effectively yielding the region to Russian forces which stormed one of Kiev's last bases there.

Obama, who has imposed tougher sanctions on Moscow than European leaders over its seizure of the Black Sea peninsula, will seek support for his firm line at a meeting with other leaders of the G7 - a group of industrialized nations that excludes Russia, which joined in 1998 to form the G8.

Since the emergency one-hour G7 meeting was announced last week, Putin has signed laws completing Russia's annexation of the region.

In what has become the biggest East-West confrontation since the Cold War, the United States and the European Union have imposed visa bans and asset freezes on some of Putin's closest political and business allies. But they have held back so far from measures designed to hit Russia's wider economy.